3 Answers
3

The first thing I would try is before you turn your computer on: plug in the monitor cable to the AGP-card - and nothing to the port of the on-board card.

You could try to disable the on-board graphics adapter. Read how you to do that in the documentation that came with your motherboard. You'll have to either set a physical jumper or a software BIOS setting, be sure you know the correct jumper (often labeled on the PCB, or how to change settings in your systems' BIOS.

Sometimes there is a setting in BIOS that allows the user to set either a PCI card or AGP card as the primary video device.

I don't believe you can run multiple monitors of separate graphics cards. At least, you can't do it in XP.
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EvilChookieJul 19 '09 at 10:30

1

@EvilChookie - you can use multiple monitors on separate graphics card since Windows 98. What you can't do is mixing embedded video and plugged cards - you have te use card with many outputs and/or multiple cards at once. Works like a charm for thousands of users.
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Tomek Z.Aug 16 '09 at 17:40